In order to achieve properties of organic polymers such as formability and flexibility and properties of inorganic materials such as heat resistance, wear resistance, and surface hardness, studies on blending inorganic fine particles to organic polymers have been widely conducted.
For example, according to a design that utilizes the properties inherent to inorganic materials, a higher compounding effect can be expected from blending inorganic fine particles having smallest possible particle size at a high concentration. This is because the smaller the particle size, the larger the surface area of the inorganic fine particles per unit weight and the wider the interface regions between organic polymers and inorganic materials. When the concentration of the inorganic fine particles is high, the properties of the inorganic materials can be more strongly exhibited.
Most of such blend systems of organic polymers and inorganic fine particles use liquid organic polymers, monomers which are starting materials for organic polymers, organic solvents, and the like, and are available as liquid products such as paints and inks from the viewpoint of coating and handling ease. Meanwhile, it is also known that when such inorganic fine particles are blended into dispersion media at high concentrations, it is difficult to obtain stable dispersion liquids and various problems arise during manufacturing processes and adversely affect the value of products obtained by the processes. In other words, inorganic fine particles of extremely small particle size have high surface activity and thus undergo secondary aggregation, resulting in problems such as low dispersion stability due to the secondary aggregates and lack of uniformity of properties such as coating film properties differing among parts of coating films.
Examples of known techniques of dispersing inorganic fine particles such as silica in organic polymers include a method with which inorganic fine particles surface-treated with a coupling agent are dispersed in a resin (refer to PTL 1), a method with which inorganic fine particles are dispersed by using a surfactant (refer to PTL 2), and a method with which inorganic fine particles are dispersed by using a mixture of a lactone-modified carboxyl-group-containing (meth)acrylate and caprolactone of (meth)acrylic acid (refer to PTL 3).
PTL 1: Japanese Examined Patent Application Publication No. 7-98657
PTL 2: Japanese Examined Patent Application Publication No. 8-13938
PTL 3: Japanese Unexamined Patent Application Publication No. 2000-281934
PTL 4: International publication No. 96/035755 pamphlet
PTL 5: Japanese Unexamined Patent Application Publication No. 2006-328354